Geology Reference
In-Depth Information
B.2.44 Osmium and Iridium
Osmium is a silvery metal of the platinum group metals. It has the distinction of
being the most dense of all the naturally occurring elements. Its main application
is as an alloy with other platinum group metals.
Iridium is a transition metal, likewise belonging to the platinum family. It is
notable for being the most corrosion resistant element known to Man. Demand
for iridium derives predominately from the electronic, automotive and chemical
industry, where it is used in catalysts and to coat electrodes in the chlor-alkali
process
Both osmium and iridum are very rare metals. Osmium is usually found in
combination with iridium and ruthenium. The most important ores for both metals
are iridosmine and osmiridium.
B.2.45 Palladium
Palladium is a silver-white metal belonging to the platinum group metals. It is
usually associated with the other PGMs and occurs either in its native form or
as a sulphide or arsenide in Ni, Cu and Fe sulphide ores. Much of it, however,
is extracted with chromite or as a byproduct of the copper-nickel ores such as
chalcopyrite, pyrrhotite and pentlandite.
Palladium is increasingly employed in electrical appliances in the form of multi-
layer ceramic capacitors. Due to its resistance to corrosion, a major use of palladium
is in those alloys employed in low voltage electrical contacts. It is also used as a
catalyst for reducing car exhaust emissions, where it replaces platinum. It can also
be alloyed to a certain extent for use in jewellery.
B.2.46 Phosphorous
Phosphorous is a nonmetal element of the nitrogen group. It is an abundant mi-
neral on Earth with all its known terrestrial minerals, orthophosphates. Some 200
crystalline phosphate minerals have been identified but by far the major amount
of P occurs in the family of apatites and these are incidently the only ones of
industrial importance. Common members are fluorapatite Ca
5
(PO
4
)
3
F, chlorap-
atite Ca
5
(PO
4
)
3
Cl and hydroxylapatite Ca
5
(PO
4
)
3
OH. In addition, there are
vast deposits of the amorphous phosphate rock phosphorite, which approximates in
composition to fluoroapatite.
Its concentrated acids are used in fertilisers for agriculture and farm production.
Phosphates are also used for special glass, sodium lamps, in steel production, in
military applications, pyrotechnics, pesticides, toothpastes or detergents.
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